Precision machine vision inspection systems (or “vision systems” for short) can be utilized to obtain precise dimensional measurements of inspected objects and to inspect various other object characteristics. Such systems may include a computer, a camera, and optical system, and a precision stage that is movable in multiple directions to allow workpiece inspection. One exemplary prior art system that can be characterized as a general-purpose “off-line” precision vision system is the commercially available QUICK VISION® series of PC-based vision systems and QVPAK® software available from Mitutoyo America Corporation (MAC), located in Aurora, Ill. The features and operation of the QUICK VISION® series of vision systems and the QVPAK® software are generally described, for example, in the QVPAK 3D CNC Vision Measuring Machine User's Guide, published January 2003, and the QVPAK 3D CNC Vision Measuring Machine Operation Guide, published September 1996, each of which is hereby incorporated by reference in their entirety. This type of system is able to use a microscope-type optical system and move the stage so as to provide inspection images of either small or relatively large workpieces at various magnifications.
General purpose precision machine vision inspection systems, such as the QUICK VISION™ system, are also generally programmable to provide automated video inspection. Such systems typically include GUI features and predefined image analysis “video tools” such that operation and programming can be performed by “non-expert” operators. For example, U.S. Pat. No. 6,542,180, which is incorporated herein by reference in its entirety, teaches a vision system that uses automated video inspection including the use of various video tools. Exemplary video tools include edge location tools, which are sometimes referred to as “box tools,” which are used to locate an edge feature of a workpiece. For example, commonly assigned U.S. Pat. No. 7,627,162, which is incorporated herein by reference in its entirety, teaches various applications of box tools.
The machine control instructions, including the specific inspection event sequence (i.e., how to acquire each image and how to analyze/inspect each acquired image), are generally stored as a “part program” or “workpiece program” that is specific to the particular workpiece configuration. For example, a part program defines how to acquire each image, such as how to position the camera relative to the workpiece, at what lighting level, at what magnification level, etc. Further, the part program defines how to analyze/inspect an acquired image, for example, by using one or more video tools such as edge/boundary detection video tools.
Video tools (or “tools” for short) and other graphical user interface features may be used manually to accomplish manual inspection and/or machine control operations (in “manual mode”). Their set-up parameters and operation can also be recorded during learn mode in order to create automatic inspection programs or “part programs”. Video tools may include, for example, edge/boundary detection tools, auto focus tools, shape or pattern matching tools, dimension measuring tools, and the like.
Various methods are known for locating edge features in workpiece images. For example, various algorithms are known that apply brightness gradient operators to images that include an edge feature to determine its location, e.g., a Canny Edge detector or a differential edge detector. Such edge detection algorithms may be included in the machine vision inspection systems that also use carefully configured illumination and/or special image-processing techniques to enhance brightness gradients or otherwise improve edge location accuracy and repeatability.
Some machine vision systems (e.g., those utilizing the QVPAK® software described above) provide edge location video tools that have adjustable parameters for an edge detection algorithm. In certain implementations, the parameters may initially be determined for an edge on a representative workpiece during a learn mode operation and then utilized during a run mode operation to find the corresponding edge of a similar workpiece. When desirable edge detection parameters are difficult or impossible to determine automatically during the learn mode, the user may choose to adjust the parameters manually. However certain edge detection parameters (e.g., thresholds such as TH, and THS, outlined herein) are considered to be difficult to understand for the majority of users (e.g., relatively unskilled users), and how their adjustment affects a particular edge detection operation is considered difficult to visualize. The adjustments of the parameters may be further complicated by the variety of edge conditions and workpiece materials in part-to-part variations encountered when programming and using general purpose machine vision inspection system. An improved method and system that allows relatively unskilled users to adjust the parameters of edge location video tools so that they can be used to reliably inspect a variety of types of edges would be desirable. More specifically, a method and system are desirable for improving the reliability of edge detection in a region of interest that includes a plurality of edges.